“Democracy is the way that we have diverse societies that don’t kill each other, largely,” Lilliana Mason, a leading scholar of partisanship, observed recently. She added: “As soon as we stop believing in it, it disappears.” Dr Mason’s own research suggests that there is sharply rising tolerance of political violence. On Wednesday, it claimed one more victim.

The shocking killing of the co-founder of Turning Point USA Charlie Kirk, a hugely influential activist who rallied young people to Donald Trump’s cause and far-right ideology more broadly, has been widely and rightly condemned across the political spectrum. Leading Democrats and progressive activists made clear that such violence must not be tolerated.

Before a perpetrator had even been identified, the president, like several other Republicans, blamed “radical left political violence”, claiming that liberal rhetoric against conservatives was “directly responsible for the terrorism that we’re seeing in our country”. Mr Trump himself faced two attempts on his life last year. He cited other victims, but not the many Democrats who have........

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